The present invention relates to over-current protection devices, and more specifically to over-current protection devices for preventing over-current faults caused by excessive load currents and short-circuit faults.
Switched-mode power supplies (SMPS) are employed in a variety of applications to convert incoming supply (typically direct current) to a particular output voltage (typically direct current) for consumption by a load. A number of well-known configurations may be employed to implement a SMPS, such as buck, boost, buck-boost, flyback, etc. In each of these configurations, a switch employed by the SMPS is selectively controlled (i.e., turned ‘on’ and ‘off’) to dictate the output generated.
Changes in the load and/or fault conditions can result in the SMPS generating excessive output currents (i.e., over-current condition). To prevent excessive currents from damaging components, prior art SMPSs have included over-current protection circuits that limit the ‘on’ time of the switch in response to the monitored current exceeding a threshold value. However, for short-circuit faults, the current built-up during the minimum ‘on’ time of the switch may exceed the current discharged during the ‘off’ time. As a result, the current supplied by the SMPS continues to increase with each successive cycle.